netdev - Re: [PATCH 03/14] net: tcp_memcontrol: properly detect ancestor socket pressure

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Date:	Sat, 14 Nov 2015 10:15:18 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	netdev@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...com
Subject: Re: [PATCH 03/14] net: tcp_memcontrol: properly detect ancestor
 socket pressure

On Sat, Nov 14, 2015 at 03:45:52PM +0300, Vladimir Davydov wrote:
> On Thu, Nov 12, 2015 at 06:41:22PM -0500, Johannes Weiner wrote:
> > When charging socket memory, the code currently checks only the local
> > page counter for excess to determine whether the memcg is under socket
> > pressure. But even if the local counter is fine, one of the ancestors
> > could have breached its limit, which should also force this child to
> > enter socket pressure. This currently doesn't happen.
> > 
> > Fix this by using page_counter_try_charge() first. If that fails, it
> > means that either the local counter or one of the ancestors are in
> > excess of their limit, and the child should enter socket pressure.
> > 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> Reviewed-by: Vladimir Davydov <vdavydov@...tuozzo.com>

Thanks Vladimir!

> For the record: it was broken by commit 3e32cb2e0a12 ("mm: memcontrol:
> lockless page counters").

I didn't realize that.

Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
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